December, 2016


www.us- tech.com


Page 21


Organic Silicone Coatings for Next-Gen Medical Devices Continued from previous page


here a coating to the surface. In these cases, HMD- SO can be used as an intermediate layer to im- prove the adhesion between a coating and the sub- strate. Guide wires are a good example. To ease in-


sertion, stainless steel guide wires are often coated with proprietary surface coatings to lubricate them. By applying a thin layer of silicon dioxide, the coating then grafts nicely to a stainless sur- face.


Organic silicones can also be applied as a


linking chemistry between other difficult-to-ad- here to surfaces such as ceramics and PTFE (Teflon). Drug delivery devices that utilize ceram- ic nozzles with micron-sized openings can become clogged and are often coated with PTFE to prevent such occurrences. Depositing a 100-150 nm layer of HMDSO promotes the bond between the two substances.


Anticorrosion Protection Anticorrosion is becoming in-


creasingly important in medical de- vices, particularly to protect the small microelectronic circuit boards used today in products or implanted in the body such as hearing aids, in- traocular devices, implantable sen- sors and pacemakers. To protect electronics against


corrosion, HMDSO coatings are ap- plied in a relatively thick coating of a micron or more. HDMSO is water and gas repellent – properties that are required to prevent corrosion. A thin layer (100 nm or so) of PTFE can also be applied if the HMDSO will be exposed to harsh chemical acids or bases.


Hydrophobic/Hydrophilic Surfaces


For vascular surgical tools and


instruments that may become fouled with tissue debris or blood, a plasma enhanced chemical deposition tech- nique can provide a coating that keeps the surgeon’s tools cleaner for longer periods of time. This is typically accomplished


by applying a hydrophobic (water-re- pellent) coating that repels water or biological fluids like blood. When used on vascular surgical devices, blood and tissue sheets off very easi- ly so that the surgeon can see more easily when cutting, for example. At the other end of the spectrum


are hydrophilic (affinity to water) de- vices. Depending on what is required, organic silicones can be used to create such surfaces with either polar or dis- persive surface energy. Potential ap- plications include coating polypropy- lene or polystyrene plates with alco- hol or to facilitate protein bonding to the surface.


Antimicrobial Surfaces There are many strategies to


achieve an anti-microbial surface, which include cell harpoons, amphi- pathic surfaces, antiseptics bound to the surface, and non-stick coatings. In a unique application, chemi-


cal vapor deposition is being used to embed nanosilver particles in a thin layer of organic silicone to prevent microbial adhesion and protect against corrosion. Nanosilver, or col- loidal silver, has been known for its antimicrobial effects from the earliest days of its use. Using a PECVD process, the tiny silver ions can be embedded in a thin layer of silicon dioxide to kill any bacteria present.


Fine-Tuning PECVD Application Despite the flexibility of


PECVD-applied organic silicones, developing the precise chemistries, added gases and even plasma equipment design requires a close, collaborative relationship between medical device designers and equipment manufacturers. Because MicroVention already had an estab-


lished relationship with PVA TePla – several of its plasma chambers were already being used to aid coating adhesion – Baldwin began consulting with them on a project to determine the benefits of coat- ings for stents. According to Baldwin, plasma equipment


PVA TePla inline high-capacity PECVD machine.


manufacturers fall into two categories: those that produce commercial off-the-shelf products and those that design and engineer systems to fit the needs of a specific application in order to resolve unique surface energy challenges.


Continued on page 23


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84